Integral membrane receptor proteins often play a key role in signal transduction across cell membranes in both bacteria and higher organisms. Detailed knowledge of the three-dimensional structures of these receptor proteins would undoubtedly contribute greatly to a general understanding of the molecular mechanisms of signal transduction, but formidable technical challenges prohibit the routine determination of high resolution structures for most membrane proteins at present. Therefore, computer modeling studies are proposed to generate detailed three-dimensional models for a bacterial membrane chemoreceptor, the Trg receptor from Escherichia coli, and a number of mammalian seven helix G protein-coupled receptors, including adrenergic and dopamine neurotransmitter receptors, and CCK-A peptide receptor. Several specific issues of adrenergic and dopamine receptor ligand binding and selectivity will be addressed utilizing molecular modeling techniques and existing experimental data. Molecular modeling studies and photoaffinity labeling experiments will be performed for CCK-A receptor, in collaboration with Prof. Laurence Miller at Mayo Clinic, to fully characterize agonist and antagonist binding sites. A final set of modeling studies will be undertaken in collaboration with Prof. Gerald Hazelbauer at Washington State University to generate detailed three-dimensional models for the bacterial Trg chemoreceptor. Utilizing data from sulfhydryl accessibility, crosslinking, and spin labeling studies performed by Prof. Hazelbauer's group, structures for the transmembrane and periplasmic domains of the receptor will be constructed, and models for the conformational changes associated with signal transduction will be explored. The model structures will be continually evaluated and refined using new experimental data from Prof. Hazelbauer's laboratory. The combination of detailed model building and close collaboration with experimental groups should yield useful new information about structure and signal transduction mechanisms for two distinct classes of membrane receptor proteins. Information obtained for the adrenergic, dopamine, and CCK-A receptors may also be of use in design of pharmacological agents targeted to these receptors.